A unique x-ray imaging and inspection system that combines 3D volumetric imaging and conventional 2D radiography for a complete x-ray inspection solution has been provided under the mark Digitome. For purposes of this application, the system will be referred to a “digitized tomography”. Digitized tomography technology has been used for film based 3-dimensional x-ray imaging, and has been enhanced to incorporate digital flat panel x-ray detectors, resulting in examinations being made in minutes. Its features, provide unique capabilities to view any horizontal or vertical plane, scan through the volume in 0.005″ increments and measure internal features. See Griffith U.S. Pat. No. 5,051,904 (“Computerized Dynamic Tomography System”), U.S. Pat. No. 5,070,454 (“Reference Marker Orientation System For A Radiographic Film-Based Computerized Tomography System”), and U.S. Pat. No. 5,319,550 (“High Resolution Digital Image Registration”), the disclosures of which are incorporated herein by reference.
The digitized tomography software contains what is known as the digitized tomography kernel. It is a set of software modules that are used to compute digitized tomography views. One defines the geometry by which the images are formed, the data arrays that contain the image data, and the coordinates of an object space. The resultant voxel value is returned to the calling software. It is the calling software's responsibility to resend the coordinates and store the voxel values so they produce the desired digitized tomography view foil.
From its inception, the digitized tomography kernel was based upon a digital simulation of what is known as the film mode. Referring to FIG. 1, its geometric derivation assumes the source 10 is at a canted angle with respect to the image plane 12. The object to examine is positioned centrally over the intersect 14 of the x-ray source optical axis 16 and the image plane. The object is then is stepwise rotated about an axis perpendicular to the image plane 12 and that passes through the above intersect. An x-ray image is acquired at each rotation position of the object.
In the film simulation mode, each acquired image is rotated by the same angle as was the object when it was exposed. The resulting images are stacked with their axes of rotation coincident. Finally, each image is translated radially inward from its axis of rotation by a distance related to the object level one desires to observe. The translation distance is a function of the perpendicular distance between the image plane and the view plane. Light passing through a stack of film positioned thusly will reveal the features at the desired view plane.
A similar computed combination of the data from a series of digitally acquired images will result in the same view obtained in the previously referred to film simulation mode and requires the combination of registered pixels from each of the digitized images. The method is described in Appendix A. In addition, other view foils are possible to compute simply by changing the pattern of the voxel coordinates passed to the digitized tomography kernel as well as various image enhancements. The film mode simulation digitized tomography kernel math is described in Appendix B wherein the kernel is limited to having the axis of rotation of the object perpendicular to the image plane.
Referring to FIG. 2, an alternate geometry can be useful. For example, the x-ray optical axis 16 could be perpendicular to the image plane and the axis of rotation of the object could be at another angle with respect to the image plane 12. This can allow the instrumentation to fit into a much smaller column because the source is immediately above the image plate rather than offset to the side. It can also permit larger and taller objects to be examined using a given image plate than does the current geometry. In a film mode simulation geometry, the object plane is not parallel to the film plane and the geometric magnification varies over the film plane. Methods can be provided by which a marker disk and misalignment post are placed to calibrate the alternate geometry.